The present invention generally relates to a defibrillation system including an atrial defibrillator for applying cardioverting electrical energy to the atria of a human heart in need of cardioversion. The present invention is more particularly directed to such a system having a portable communication device operable by a patient for selectably initiating atrial fibrillation detection without committing to atrial cardioverting therapy.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life-threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart, and may even experience dizziness or even loss of consciousness.
Atrial fibrillation occurs suddenly, and many times can only be corrected by a discharge of electrical energy to the heart. Implantable atrial defibrillators have become a reality to provide relief to patients suffering from occurrences of atrial fibrillation.
For example, implantable atrial defibrillators and lead systems which exhibit complete automatic operation are fully described in U.S. Pat. No. 5,282,837, issued Feb. 1, 1994, for "Improved Atrial Defibrillator and Method," U.S. Pat. No. 5,350,404, issued Sep. 27, 1994, for "Lead System for Use with an Atrial Defibrillator and Method," and U.S. Pat. No. 5,207,219, issued May 4, 1993, for "Atrial Defibrillator and Method for Providing Interval Timing Prior to Cardioversion," all of which patents are assigned to the assignee of the present invention and incorporated herein by reference. Each of these patents discloses and claims an implantable atrial defibrillator wherein atrial fibrillation is automatically detected and, when needed, cardioverting electrical energy is applied to the atria to terminate the atrial fibrillation episode and return the heart to normal sinus rhythm.
As with any implantable device, it would be desirable to be able to provide the patient with some manual control for the implanted device. For example, implantable pacemakers known in the art may be totally deactivated by placing a magnet over the implant site. The magnetic field of the magnet causes a reed switch within the implanted device to remain either open or closed as long as the magnet is held there. Other magnet modes are known for checking the power levels of the implanted device battery, for example.
While magnets have proven effective in the past, they are not convenient to use. First of all, such magnets are heavy and, in most uses, rather large, making them difficult to carry in a pocket or purse. Also, because the magnets produce a magnetic field, they can erase dictation or other type of audio tape to which they may come into close proximity within a purse or pocket. Under such conditions, they can also erase the magnetic strips on credit and bank cards. They would further erase floppy disks for computers.
Providing some manual control over an implanted atrial defibrillator is described in U.S. Pat. No. 5,490,862. There, a magnet is described for generating external commands which cause the defibrillator to enter an atrial fibrillation detection and committed therapy sequence. A magnet is certainly effective for such use. However, in addition to the drawbacks previously mentioned, magnets do not provide any means for feedback to inform the patient that the implanted device is acting upon the external command. An acknowledgment of receipt of a command and the fact that the implant is implementing the command would be important feedback to patients. This is especially true if the patient is attempting to have the implanted device initiate required therapy.
In answer to the problems resulting from the use of magnets in such systems, an atrial defibrillation system including an external communication device dimensioned to be hand-held is disclosed and claimed in U.S. Pat. No. 5,674,249 which issued on Oct. 7, 1997 for "Atrial Defibrillation System Having A Portable Communication Device," and which is incorporated herein by reference. The portable communication device there disclosed includes an RF transmitter for transmitting a command signal to the implantable defibrillator. The implantable defibrillator includes a receiver for receiving the command signals and performs a task responsive to receipt of the command signal. An RF transmitter within the implantable device transmits an acknowledgment signal back to the portable communication device upon receipt of the command signal. The portable communication device further includes a receiver which receives the acknowledgment signal and provides a perceptible indication responsive to receipt of the acknowledgment signal to the patient. In this way, the patient knows that the command was received and that the implanted device is performing the desired task.
While the last two mentioned atrial defibrillation systems go a long way towards providing effective and positive control of an implantable atrial defibrillator by the patient, they do not provide a complete answer. For example, they provide for very limited operational modalities of an automatic mode, a patient activated mode, and a combination of these two modalities. In all of these modalities, the patient is committed to cardioverting therapy if atrial fibrillation is detected. In the automatic mode, atrial fibrillation detections most often occur when the patient is not in atrial fibrillation. Many atrial fibrillation patients are highly symptomatic when experiencing atrial fibrillation. Automatic detection for these patients can represent unwarranted depletion of the defibrillator power source. Further, a patient may not be in a position to receive cardioverting therapy at a time when the committed therapy is to be delivered. At other times, a patient may simply want to confirm the absence of atrial fibrillation or be able to determine that the atrial fibrillation detector of the patient's defibrillator agrees with patient's perception of the arrhythmia. Hence, there is a need in the art for an atrial defibrillation system which enables a patient to select and activate atrial fibrillation detection without committing to cardioverting therapy.